Device for determining the level of contents in a container

ABSTRACT

A level sensor which is capable of largely eliminating the influence of structural parts and/or the formation of deposits on the measuring accuracy and on the measuring sensitivity of the level sensor. There is provided, a launching unit which has at least one length, which essentially corresponds to the distance from the container wall to the lower edge of the structural part, and which is positioned in such a manner that a transition area launching unit conductive element is located approximately in the plane of the lower edge of the structural part, with the diameter of the opening of the launching unit on the transition launching unit conductive element is in the order of magnitude of the wavelength of the high-frequency measurement signals.

FIELD OF THE INVENTION

The invention relates to a device for determining and for monitoring thelevel of contents in a container, in which on the container at least onestructural part is provided, on which or in whose surroundings at leastthe sensor-associated part of the device is mounted, having a signalgenerating unit, which generates high-frequency measurement signals,having an input unit and a conductive element, the measurement signalsbeing input to the conductive element via the input unit, and having areceiving/evaluating unit, which directly or indirectly via the transittime of the measurement signals, reflected from the surface or boundaryface of the contents, determines the level of the contents or thelocation of the boundary face in the container as generically defined bythe preamble to the independent claims. It is understood that the deviceis also suitable for determining the location of at least one boundaryface between two phases of a medium or between two media.

BACKGROUND OF THE INVENTION

For determining the level of contents in a container, measuring systemsare used that measure different physical variables. On the basis ofthese variables, the desired information about the level is thenderived. Besides mechanical scanners, capacitive, conductive orhydrostatic measuring probes are used, as are detectors that operate onthe basis of ultrasound, microwaves, or radioactive radiation.

In many fields of use, such as petrochemicals, chemistry and the foodindustry, highly accurate measurements of the level of liquids or bulkgoods in containers (tanks, silos, etc.) are needed. Increasingly,sensors are therefore used in which brief electromagnetic high-frequencypulses (TDR methods or pulse-radar methods) or continuousfrequency-modulated microwaves (such as FMCW-radar methods) are inputinto a conductive element or a waveguide and carried into the containerwhere the contents are stored by means of the waveguide. The knownvariants can be considered as the waveguide: surface waveguides on theSommerfeld or Goubau principle, or Lecher waveguides.

In physical terms, in this measuring method, the effect is exploitedthat at the boundary face between two different media, such as air andoil or air and water, some of the guided high-frequency pulses or theguided microwaves carried are reflected because of the abrupt change(discontinuity) in the dielectric constants of both media and isreturned back to a receiver by way of the conductive element. Thereflected component (or useful echo signal) is all the greater, thegreater the difference between the dielectric constants of the twomedia. The distance from the surface of the contents can be determinedfrom the transit time of the reflected component of the high-frequencypulses or CW signals (echo signals). If the empty distance of thecontainer is known, then the level of contents in the container can becalculated. If a boundary face determination is to be performed, thenthe location of the boundary face can be determined from the outcomes ofthe measurement.

Sensors with guided high-frequency signals (pulses or waves) aredistinguished over sensors that freely broadcast high-frequency pulsesor waves (free-field microwave systems or FMR, also called “genuineradar systems”) in having a substantially greater echo amplitude. Thereason for this is that the power flow is effected quite purposefullyalong the waveguide or conductive element. Moreover, sensors with guidedhigh-frequency signals have greater measuring sensitivity and measuringaccuracy at close range than freely broadcasting sensors.

The measuring accuracy and measuring sensitivity of sensors that usesurface or Lecher waveguides is worsened considerably if the transitionregion from the input unit to the conductive element is located in theregion of a container connection stub or—in general terms—in the regionof a structural part that is disposed in the container. If that is thecase, then there is the risk that the portion of the radiation that isnot guided—as desired—in the direction of the surface of the contentsbut instead is broadcast toward the side will lead to transverseresonances (or in the case of a connection stub, to void resonances).Moreover, because of the surface waves along the conductive element,longitudinal resonances can develop. The interfering echo signals thatthis causes can become so strong that the actual useful echo signal isno longer detectable. Moreover, if longitudinal resonances occur fromreflection in the propagation direction, the attenuation of theamplitude of the surface wave and hence of the useful echo signal isespecially problematic.

One problem that occurs in particular—but not exclusively—when thesensor is secured in the connection stub of a container is thedevelopment of deposits. These occur especially in containers that arefilled with hot media or in containers located outdoors that are exposedto major temperature fluctuations. When dust additionally develops inthe container, a deposit then forms that can grow over time to such anextent that the transmission of the surface waves is entirelysuppressed, or that at least interfering echo signals at close range arecreated.

SUMMARY OF THE INVENTION

An object of the invention is to provide a device which is capable oflargely eliminating the influence that a structural part and/or theformation of deposits on the sensor has on the measuring accuracy andmeasuring sensitivity of the sensor.

In a first embodiment of the device of the invention, this object isattained in that the input unit has at least a length that correspondsessentially to the spacing from the container wall to the lower edge ofthe structural part and is positioned such that the transition region“input unit conductive element” is located approximately in the plane ofthe lower edge of the structural part; and that the diameter of theopening of the input unit at the transition region “inputunit—conductive element” is on the order of magnitude of the wavelengthof the high-frequency measurement signals. Because the input unit islengthened according to the invention, the structural parts are locatedoutside the region into which electromagnetic energy is broadcast. Thegeneration of void resonances and interference signals is thereforelargely prevented. A further essential characteristic of the inventionis that the opening or aperture of the input unit is on the same orderof magnitude as the wavelength of the measurement signals. This assuresthat the input unit has a pronounced directional characteristic, and themeasurement signals are for the most part input to the conductiveelement and thus are not extended back in the opposite direction alongthe input unit or broadcast laterally.

In an alternative embodiment of the device of the invention, the objectis attained in that the input unit has a predetermined length, and ispositioned in the container such that the opening of the input unit,pointing in the direction of the medium, has a certain spacing from thecorresponding container wall; and that the diameter of the opening ofthe input unit at the “input unit—conductive element” transition is onthe order of magnitude of the wavelength of the high-frequencymeasurement signals. This arrangement is especially advantageous if,although no structural parts that could adversely affect the propagationof the measurement signals are located in the vicinity of the inputunit, nevertheless there is still an increased risk that from condensateformation and dust production in the container interior, deposits couldform on the input unit. The length and input shifts the transitionregion between the input unit and the conductive element to a pointlocated farther in the interior of the container, which experienceteaches is less vulnerable to the development of deposits.

An advantageous version of the two embodiments of the invention recitedabove provides that the input unit has an inner conductor and an outerconductor; and that between the inner conductor and the outer conductor,in at least a partial region, a dielectric material is disposed. Sincethe field symmetry in the coaxial cable is quite similar to the fieldsymmetry in a Sommerfeld or Goubau conductor, at the transition region“input unit—conductive element” only slight field interference occurs,which is expressed in a high transmission rate and thus high measuringsensitivity. Because of the low proportion of reflected measurementsignals, the interference at close range is also low, since multiplereflections between locally lengthy interference points are avoided. Theinterference points are on the one hand the plug on the electronics, forinstance, and on the other the transition region “input unit—conductiveelement”. Other advantages of this version are considered to be that thedielectric material seals off the level sensor from the container, andalso serves to mechanically retain the inner conductor. If condensateformation in the voids of the input need not be feared, then it ispossible, for reasons of cost, to dispense with completely filling thethree-dimensional region between the inner conductor and the outerconductor with dielectric material.

It has moreover proved especially advantageous if the dielectricmaterial of the input unit is essentially tapered from the transitionregion “input unit—conductive element” onward, and an upper portion ofthe conductive element is disposed approximately in the region of thelongitudinal axis of the taper. The tapered form of the dielectricmaterial at the same time has several advantages:

1. Because of the tapered form, the phase front at the transition region“input unit—conductive element” is changed in such a way that animproved directional effect is obtained. Thus on the one hand theundesired broadcasting to the side and to the back is reduced, while onthe other hand the input to the waveguide is improved. Because of thefirst above advantage, the incidence of interfering echoes and so-calledconnection stub ringing is reduced, while because of the secondadvantage above, an increase in the amplitude of the useful echo signalis attained.

2. Because of the tapered shape, it is attained that signal componentsreflected from different points of the taper interfere with one anotherdestructively, which leads to a reduction in the block distance. Theterm “block distance” is understood to be the minimum measurabledistance of a level sensor.

3. Because of the tapered shape, the outflow of condensate droplets isfacilitated; this lessens the risk of the formation of deposits.

In a preferred version of the two variants named above for attaining theobject of the invention, it is proposed that the outer conductor of theinput unit changes over, essentially from the transition region “inputunit conductive element” onward into a horn-shaped element, and an upperportion of the conductive element is disposed approximately in theregion of the longitudinal axis of the taper. The advantages of thisversion are as follows:

1. Because of the enlarged aperture of the horn, the directional actionis improved considerably.

2. The horn reduces field distortion in the transition region “inputunit—conductive element”, since the outer conductor does not drop awayabruptly but instead widens continuously in diameter. Ideally, thediameter is so large that the surface wave mode already detaches fromthe outer conductor. As a result, there is little field interference atthe transition region “input unit—conductive element”.

3. Condensate can flow off on the outside of the horn, so that the crosssection within which the signal is guided is not closed by deposits.

In a third embodiment of the device of the invention, the object isattained in that the transition region “input unit—conductive element”is located essentially in the plane of the container wall; the inputunit has an inner conductor and an outer conductor; that between theinner conductor and the outer conductor, in at least a partial region, adielectric material is disposed; and the dielectric material of theinput unit is essentially tapered from the transition region “inputunit—conductive element” onward, and an upper portion of the conductiveelement is disposed approximately in the region of the longitudinal axisof the taper. In this embodiment as well, the diameter of the apertureof the input unit is preferably on the order of magnitude of thewavelength of the measurement signals.

In a variant of the device of the invention, the object is attained inthat the transition region “input unit conductive element” is locatedessentially in the plane of the container wall; the input unit has aninner conductor and an outer conductor; that between the inner conductorand the outer conductor, in at least a partial region, a dielectricmaterial is disposed; and the outer conductor of the input unit changesover, essentially from the transition region “input unit—conductiveelement” onward into a horn-shaped element, and an upper portion of theconductive element is disposed approximately in the region of thelongitudinal axis of the taper. Once again, preferably the diameter ofthe aperture of the input unit is on the order of magnitude of thewavelength of the measurement signals.

The advantages of these last two versions, with a taper or a horn-shapedelement, have already been explained above. Both versions are preferablyused whenever there are no interfering structural parts positioned inthe vicinity of the device of the invention, yet it is important not todispense with the advantages of the invention, particularly with a viewto improved directional action, optimized transmission, and reduceddeposit formation. Because the measurement signals are input to theconductive element by means of the horn-shaped element and/or by meansof a taper, however, an adequately good directional action is attainedeven if “interference points” can be found in the immediate vicinity ofthe transition region “input unit—conductive element”. It is naturallynot unimportant here that a taper and/or a small horn-shaped element isless expensive than a “artificially” lengthened input unit.

A preferred version of the two variants named above of the device of theinvention therefore provides that the transition region “inputunit—conductive element” is positioned essentially in the plane of thetop side of a structural part, in particular a connection stub, providedon the container.

In the fifth embodiment of the device of the invention, the object isattained in that in the region of the side walls of the structural partand in the region of the underside of the structural part, a conductivematerial is disposed; and that the transition region “input unitconductive—element” is positioned approximately in the plane in whichthe lower edge of the structural part is located. If the structural partis for instance a connection stub, then it is attained by this versionthat no electromagnetic energy can get into the connection stub.Consequently, no void resonances are generated, either, which has afavorable effect on the block distance. Moreover, this version reducesthe risk of deposit formation in the critical region of the TDR sensorto a minimum.

An advantageous refinement of the device of the invention recited aboveproposes that a cup-shaped insert part is insertable into the connectionstub, and the insert part is coated on at least one side with aconductive material, or the insert part is made from a conductivematerial.

In an advantageous refinement of the device of the invention, an openingfor receiving the level sensor is provided on the underside of theinsert part. This makes it possible to use the same measuring instrumentfor different installation situations. Only the cup has to be adapted tothe dimensions of the connection stub.

Moreover, one version of the device of the invention provides a coverpart, which closes off the top side of the connection stub and of theinsert part. This protects the electronics of the measuring instrument,since no dirt or water, for instance, can collect in the top. Moreover,even with narrow connection stubs, it is possible to mount the levelsensor in such a way that the indicator and/or control elements of thesensor remain accessible.

In a sixth embodiment of the device of the invention, the object isattained in that the input unit has a length which is essentiallyequivalent to the spacing from the container wall to the lower edge ofthe structural part; that the input unit is positioned such that thetransition region “input unit—conductive element” is locatedapproximately in the plane of the lower edge of the structural part; andthat disposed on the underside of the connection stub in the transitionregion “input unit—conductive element” is a platelike element, which atleast on the side toward the medium in the container is electricallyconductive. This variant of the invention is considered especiallyeconomical.

An advantageous refinement of the device of the invention, incombination with the variant described above, provides electricalconnecting elements, which are disposed in the region of the outer edgesof the platelike element and in the region of the connection stub. Thepreferably resilient contact elements assure a high-frequency-tightclosure between the plate and the connection stub. Consequently, therisk that some of the energy of the transmitted signals will bereflected back into the connection stub and there induce the highlyunwanted void resonances, is quite low.

In a seventh embodiment of the device of the invention, the object isattained in that the transition region “input unit—conductive element”is disposed in the plane in which the top side of the structural part islocated; that the conductive element is modified, approximately over thelength of the structural part or over the length that is equivalent tothe distance between the corresponding container wall and the lower edgeof the structural part, in such a way that in this region virtually nointeractions occur between the measurement signals, carried along theconductive element, and the structural part.

An advantageous refinement of the device of the invention provides thatthe conductive element, over the length that is equivalent to thedistance between the corresponding container wall and the lower edge ofthe structural part, is made from a material of low electricalconductivity and/or high magnetic permeability.

It is also provided that the surface of the conductive element, over thelength of the structural part or over the length that is equivalent tothe distance between the corresponding container wall and the lower edgeof the structural part, has a roughened surface structure. Alternativelyor in addition, it is provided the surface of the conductive element,over the length of the structural part or over the length that isequivalent to the distance between the corresponding container wall andthe lower edge of the structural part, has a surface structure by whichthe longitudinal inductance of the conductive element is increased. Asan example, a helical surface structure can be named.

One advantageous version of the device of the invention is considered tobe that the conductive element, over the length of the structural partor over the length that is equivalent to the distance between thecorresponding container wall and the lower edge of the structural part,has an insulating layer, whose magnetic and/or dielectrical propertiesare dimensioned such that the length of the electromagnetic fields islimited to the region at close range to the conductive element.

The aforementioned versions are distinguished by the fact that the fieldlength is reduced in a targeted way in those regions where there is arisk of an unwanted interaction with built-in fittings, but not over theremaining length of the conductive element. Here, especially if depositsform on the conductive element, a short field length would lead tosevere damping of the measurement signals.

In an eighth embodiment of the device of the invention, the object isattained in that the transition region “input unit—conductive element”is disposed in the plane of the container wall; that the conductiveelement, at least in the upper region, is made from a material of lowelectrical conductivity and/or high magnetic permeability; and/or thatthe conductive element at least in the upper region has a roughenedsurface structure; and/or that the conductive element at least in theupper region has a surface structure by which the longitudinalinductance of the conductive element is increased; and/or that theconductive element at least in the upper region has an insulating layer,whose magnetic and/or dielectric properties are dimensioned such thatthe length of the electromagnetic fields is limited to the region atclose range to the conductive element.

These variants of the embodiment of the invention have essentially twodecisive advantages:

The directional action is improved, since because of the lesser fieldlength, the aperture is effectively increased and the directionalcharacteristic is improved. Thus there are fewer problems fromelectromagnetic fields broadcast laterally into the container, whichafter multiple reflections in the container could cause an interferingbackground. Moreover, because of the lesser field length of themeasurement signals traveling along the conductive element, the abruptchange in wave resistance at the transition from the input unit to theconductive element is ameliorated. This is expressed in a highertransmission rate, and thus a lower reflection rate, of the measurementsignals.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described in further detail in conjunction withthe following drawings. Shown are:

FIG. 1: a schematic illustration of a first embodiment of the device ofthe invention;

FIG. 2: a schematic illustration of a second embodiment of the device ofthe invention;

FIG. 3: a schematic illustration of a third embodiment of the device ofthe invention;

FIG. 4: a schematic illustration of a fourth embodiment of the device ofthe invention;

FIG. 5: a schematic illustration of an advantageous version of theembodiment of the device of the invention shown in FIG. 3;

FIG. 6: a schematic illustration of an advantageous version of theembodiment of the device of the invention shown in FIG. 4;

FIG. 7: a schematic illustration of a fifth embodiment of the device ofthe invention;

FIG. 8: a schematic illustration of an advantageous version of theembodiment of the device of the invention shown in FIG. 7;

FIG. 9: a schematic illustration of a sixth embodiment of the device ofthe invention;

FIG. 10: a schematic illustration of a seventh embodiment of the deviceof the invention;

FIG. 11: a schematic illustration of an eighth embodiment of the deviceof the invention; and

FIG. 12: a schematic illustration of a preferred version of theconductive element.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a schematic illustration of a first embodiment of the levelsensor 1 of the invention. The level sensor comprises a transceiver 29,a coaxial cable, an input unit 2, and a conductive element 7. Theevaluation of the echo signals is done in an evaluation unit, not shownseparately in FIG. 1.

In the case shown, the input unit 2 has a length that is greater thanthe length of the connection stub 4. The input unit 2 is disposed suchthat the opening 8 is in the vicinity of—in this case, below—the loweredge 5 of the connection stub 4. It is understood that the opening 8 canalso be placed above the lower edge 5. Moreover, the opening 8 in theinput unit 2 is dimensioned such that it is on the order of magnitude ofthe wavelength of the measurement signals guided by the level sensor 1.To a very great extent, the embodiment according to the inventionprevents components of the measurement signals from entering theconnection stub 4. Consequently, virtually no void resonances areexcited, which is expressed in a considerable improvement in themeasuring accuracy of the level sensor 1. In the case shown, thethree-dimensional region between the inner conductor 9 and the outerconductor 10 is furthermore filled with a dielectric material 11. Theadvantages of this embodiment have already been explained at lengthabove and will not be repeated here. To increase the directional actionof the level sensor 1, the dielectric material 11 is tapered, from thetransition region 6 between the input unit 2 and the conductive element7 onward. It is understood that the taper 12 can have the most variousembodiments. In FIG. 2, a schematic illustration of a second embodimentof the device of the invention is shown, which essentially differs fromthe version shown in FIG. 1 only in that it is disposed not in aconnection stub 4 but rather directly on the contained wall 3. Theadvantages of this embodiment of the invention have also already beenaddressed in detail above.

A schematic illustration of a third embodiment of the device of theinvention can be seen in FIG. 3. Here, the transition region 6 betweenthe input unit 2 and the conductive element 7 is disposed such that itis located virtually in the plane of the container wall 3. The inputunit 2 has an inner conductor 9 and an outer conductor 10. Between thetwo parts, a dielectric material 11 is disposed. The dielectric material11 of the input unit 2 is tapered, approximately from the transitionregion 6 “input unit 2—conductive element 7” onward, and an upperportion of the conductive element 7 is disposed approximately in theregion of the longitudinal axis of the taper 12. As the primaryadvantages of this embodiment, the excellent directional action, theshort block distance, and the reduced risk of deposit formation can benamed. To improve the directional action still further, the outerconductor 13 is widened, from the transition region 6 “input unit2—conductive element 7” onward, into a horn-shaped element 13.

In FIG. 4, a schematic illustration of a fourth embodiment of the deviceof the invention is shown. Once again, the transition region 6 “inputunit 2—conductive element 7” is disposed such that it is locatedvirtually in the plane of the container wall 3. The input unit 2comprises an inner conductor 9 and an outer conductor 10, and adielectric material 13 can be found between the inner conductor 9 andthe outer conductor 10. As already noted above, it is unnecessary forthe dielectric material 11 to fill the entire three-dimensional regionbetween the inner conductor 9 and the outer conductor 10. The outerconductor 10 of the input unit 2 is widened, approximately from thetransition region 6 “input unit 2—conductive element 7” onward, in sucha way that it forms a horn-shaped element 13. An upper portion of theconductive element 7 is disposed approximately in the region of thelongitudinal axis of the horn-shaped element 13. Since the advantages ofthis embodiment have already been described at length above, it sufficesat this point to list them briefly: improved directional action, reducedfield distortion at the transition region 6 “input unit 2—conductiveelement 7”, and thus an increased transmission rate and greatly reducedrisk of deposit formation.

The embodiments shown in FIGS. 5 and 6 correspond to those of FIGS. 3and 4, except that here the level sensors 1 are disposed in theconnection stub 4 of a container 3.

It is quite favorable if the input unit 2 is placed in a greatlyextended metal plate. The metal plate improves the electrical adaptationof the conductive element 7 and prevents the broadcasting ofelectromagnetic energy to the rear. The metal plate acts on the order ofan electrical mirror.

FIG. 7 is a schematic illustration of a fifth embodiment of the deviceof the invention. A connection stub 4 is provided in the container wall3. A conductive material 20 is disposed on the side walls 17, 18 and inthe region of the underside 19 of the connection stub 4. Preferably,this is a cup-shaped insert element 21, which is adapted to thedimensions of the connection stub 4.

The level sensor 1, comprising the transceiver 29, input unit 2, andconductive element 7, is embodied in this case shown as a compact sensorand is positioned in an opening 22 on the underside 19 of the cup-shapedinsert element 21. The input unit 2 is positioned in the connection stub4 in such a way that the transition region 6 “input unit 2—conductiveelement 7” comes to be located essentially in the plane of the containerwall 3. It is understood that for the sake of exhausting theaforementioned advantages, it is also possible to provide a taper 12and/or a horn-shaped element 13 in addition at the transition region 6“input unit 2—conductive element 7”.

FIG. 8 shows a schematic illustration of an advantageous version of theembodiment of the device of the invention shown in FIG. 7. It differsfrom the variant shown in FIG. 7 essentially only in the cover part 23,which closes off the cup-shaped insert part 21, disposed in theconnection stub 4, from the outside. This version will always be usedwhenever the TDR sensor 1 on the one hand is to be protected againstenvironmental factors, yet its control and display elements need toremain readily accessible.

In FIG. 9, a schematic illustration of a sixth embodiment of the deviceof the invention can be seen, which is distinguished by low productioncosts. The input unit 2 has a length which is essentially equivalent tothe length of the connection stub 4. The input unit 2 is positioned suchthat the transition region 6 “input unit 2—conductive element 7” islocated approximately in the plane of the lower edge 5 of the connectionstub 4. In the transition region 6 “input unit 2—conductive element 7”,on the underside 19 of the connection stub 4, a platelike element 24 isdisposed, which is electrically conductive at least on the side orientedtoward the contents in the container. In the region of the outer edges26 of the platelike element 24, connecting elements 25 of anelectrically conductive material are provided. These connecting orcontact elements 25 are preferably embodied resiliently. They assure ahigh-frequency-tight closure between the platelike element 24 and theconnection stub 4, whose side walls 17, 18 are either made from anelectrically conductive material or at least lined with an electricallyconductive material. As a result, as already noted several times, therisk that some of the energy of the transmission signals will get backinto the connection stub is reduced.

FIG. 10 shows a schematic illustration of a seventh embodiment of thedevice of the invention. The transition region 6 “input unit2—conductive element 7” is disposed in the plane in which the top side16 of the connection stub 4 is located. The conductive element 7 ismodified, approximately over the length of the connection stub 4 (or ingeneral terms, over the length that is equivalent to the distancebetween the corresponding container wall 3 and the lower edge 5 of therespective structural part or built-in part), in such a way that in thisregion, virtually no interactions occur between the measurement signals,guided along the conductive element 7, and the connection stub 4 (or ingeneral the structural part). The version shown in FIG. 11 differs fromthe version shown in FIG. 10 only in that it is not secured in theregion of a connection stub 4.

There are many possibilities by way of which—each taken by itself, or incombination with at least one other variant—the aforementioned goal canbe attained:

The conductive element 7, at least in its upper region, is made from amaterial of low electrical conductivity and/or high magneticpermeability;

the conductive element 7, at least in the upper region, has a roughenedsurface structure;

the conductive element 7, at least in the upper region, has a surfacestructure by which the longitudinal inductance of the conductive elementis increased;

the conductive element 7, as explicitly shown in FIG. 10 and FIG. 11, atleast in the upper region, has an insulating layer 28, whose magneticand/or dielectric properties are dimensioned such that the length of theelectromagnetic fields is limited to the region at close range to theconductive element 7.

In FIG. 12, a schematic illustration of a preferred embodiment of theconductive element 7 can be seen. The conductive element 7 is made froma high-permeability material, the effect of which is only a slight fieldlength of the service wave guided along the conductive element 7. Inaddition, the surface of the conductive element 7 is not smooth butinstead has a roughened structure, which likewise contributes to aconsiderable field reduction. If for instance the surface of theconductive element 7 is made helical, then an increase in thelongitudinal inductance is achieved. The wave resistance is increased,and the field length is reduced.

Moreover, at least in the region adjoining the input unit, theconductive element has an insulating layer 29, which has magnetic anddielectric properties adapted such that simultaneously the field lengthof the measurement signals guided along the conductive element 7 arereduced down to the desired amount. A further advantage of asufficiently thick insulating layer 29 is moreover that the measuringaccuracy of the level sensor 1 is virtually independent of any depositformation.

1. A device for determining and/or monitoring the level of contents, orthe location of the boundary face between two media or phases, in acontainer, in which on the container at least one structural part isprovided, on which or in whose surroundings at least a sensor-associatedpart of the device is mounted, having; a signal generating unit, whichgenerates high-frequency measurement signals, said signal generatingunit having an input unit and a conductive element, the measurementsignals being input to said conductive element via said input unit; anda receiving/evaluating unit, which directly or indirectly via thetransit time of the measurement signals, reflected from the surface orboundary face of the contents, determines the level of the contents orthe location of the boundary face in the container, wherein: said inputunit has at least a length that corresponds essentially to the spacingfrom the container wall to the lower edge of the structural part and ispositioned such that the transition region input unit—conductive elementis located approximately in the plane of the lower edge of thestructural part; and the diameter of the opening of said input unit atthe transition region input unit—conductive element is on the order ofmagnitude of the wavelength of the high-frequency measurement signals.2. A device for determining and/or monitoring the level of contents, orthe location of the boundary face between two media or phases, in acontainer, having: a signal generating unit, which generateshigh-frequency measurement signals, said signal generating unit havingan input unit and a conductive element, the measurement signals beinginput to said conductive element via said input unit; and areceiving/evaluating unit, which directly or indirectly via the transittime of the measurement signals, reflected from the surface or boundaryface of the contents, determines the level of the contents or thelocation of the boundary face in the container, wherein: said input unithas a predetermined length, and is positioned in the container such thatthe opening of said input unit, pointing in the direction of the medium,has a certain spacing from the corresponding container wall; and thediameter of the opening of said input unit at the input unit—conductiveelement transition is on the order of magnitude of the wavelength of thehigh-frequency measurement signals.
 3. The device of claim 1, wherein:said input unit has an inner conductor and an outer conductor; andbetween said inner conductor and said outer conductor, in at least apartial region, a dielectric material is disposed.
 4. The device ofclaim 1, wherein: said dielectric material of said input unit isessentially tapered from the transition region input unit—conductiveelement onward, and an upper portion of said conductive element isdisposed approximately in the region of the longitudinal axis of saidtaper.
 5. The device of claim 1, wherein: said outer conductor of saidinput unit changes over, essentially from the transition region inputunit—conductive element onward into a horn-shaped element, and an upperportion of the conductive element is disposed approximately in theregion of the longitudinal axis of said taper.
 6. A device fordetermining and/or monitoring the level of contents, or the location ofthe boundary face between two media or phases, in a container, having: asignal generating unit, which generates high-frequency measurementsignals, said signal generating unit having an input unit and aconductive element, the measurement signals being input to saidconductive element via the input unit; and a receiving/evaluating unit,which directly or indirectly via the transit time of the measurementsignals, reflected from the surface or boundary face of the contents,determines the level of the contents or the location of the boundaryface in the container, wherein: the transition region inputunit—conductive element is located essentially in the plane of thecontainer wall; said input unit has an inner conductor and an outerconductor; between said inner conductor and said outer conductor, in atleast a partial region, a dielectric material is disposed; and saiddielectric material of said input unit is essentially tapered from thetransition region input unit—conductive element onward, and an upperportion of said conductive element is disposed approximately in theregion of the longitudinal axis of said taper.
 7. A device fordetermining and/or monitoring the level of contents, or the location ofthe boundary face between two media or phases, in a container, having: asignal generating unit, which generates high-frequency measurementsignals, said signal generating unit having an input unit and aconductive element, the measurement signals being input to saidconductive element via said input unit; and a receiving/evaluating unit,which directly or indirectly via the transit time of the measurementsignals, reflected from the surface or boundary face of the contents,determines the level of the contents or the location of the boundaryface in the container, wherein: the transition region inputunit—conductive element is located essentially in the plane of thecontainer wall; said input unit has an inner conductor and an outerconductor; between said inner conductor and said outer conductor, in atleast a partial region, a dielectric material is disposed; and saidouter conductor of the input unit changes over, essentially from thetransition region input unit—conductive element onward into ahorn-shaped element, and an upper portion of the conductive element isdisposed approximately in the region of the longitudinal axis of thetaper.
 8. The device of claim 6, wherein: said transition region inputunit—conductive element is position essentially in the plane of the topside of a structural part, in particular a connection stub, provided onthe container.
 9. A device for determining and/or monitoring the levelof contents, or the location of the boundary face between two media orphases, in a container, in which on the container at least onestructural part, in particular a connection stub, is provided, in whichat least the sensor-associated part of the device is mounted, having: asignal generating unit, which generates high-frequency measurementsignals, said signal generating unit having an input unit and aconductive element, the measurement signals being input to saidconductive element via said input unit; and a receiving/evaluating unit,which directly or indirectly via the transit time of the measurementsignals, reflected from the surface or boundary face of the contents,determines the level of the contents or the location of the boundaryface in the container, wherein: in the region of the side walls of thestructural part and in the region of the underside of the structuralpart, a conductive material is disposed; and the transition region inputunit—conductive element is positioned approximately in the plane inwhich the lower edge of the structural part is located.
 10. The deviceof claim 9, wherein: a cup-shaped insert part is insertable into theconnection stub, and said insert part is coated on at least one sidewith a conductive material, or said insert part is made from aconductive material.
 11. The device of claim 9, wherein: an opening forreceiving the level sensor is provided on the underside of said insertpart.
 12. The device of claim 9, wherein: a cover part is provided,which closes off the top side of the connection stub and said insertpart.
 13. A device for determining and/or monitoring the level ofcontents, or the location of the boundary face between two media orphases, in a container, in which on the container at least onestructural part, in particular a connection stub, is provided, in or onthe connection stub at least the sensor-associated part of the device ismounted, having: a signal generating unit, which generateshigh-frequency measurement signals, said signal generating unit havingan input unit and a conductive element, the measurement signals beinginput to said conductive element via said input unit; and areceiving/evaluating unit, which directly or indirectly via the transittime of the measurement signals, reflected from the surface or boundaryface of the contents, determines the level of the contents or thelocation of the boundary face in the container, wherein: said input unithas a length which is essentially equivalent to the pacing from thecontainer wall to the lower edge of the structural part; said input unitis positioned such that the transition region input unit—conductiveelement is located approximately in the plane of the lower edge of thestructural part; and disposed on the underside of the connection stub inthe transition region input unit—conductive element is a platelikeelement, which at least on the side toward the medium in the containeris electrically conductive.
 14. The device of claim 13, wherein:electrical connecting elements are provided, which are disposed in theregion of the outer edges of the platelike element and in the region ofthe connection stub.
 15. A device for determining and/or monitoring thelevel of contents, or the location of the boundary face between twomedia or phases, in a container, in which on the container at least onestructural part, in particular a connection stub, is provided, in or onthe connection stub at least the sensor-associated part of the device ismounted, having: a signal generating unit, which generateshigh-frequency measurement signals, said signal generating unit havingan input unit and a conductive element, the measurement signals beinginput to said conductive element via said input unit; and areceiving/evaluating unit, which directly or indirectly via the transittime of the measurement signals, reflected from the surface or boundaryface of the contents, determines the level of the contents or thelocation of the boundary face in the container, the transition regioninput unit—conductive element is disposed in the plane in which the topside of the structural part is located; said conductive element ismodified, approximately over the length of the structural part or overthe length that is equivalent to the distance between the correspondingcontainer wall and the lower edge of the structural part, in such a waythat in this region virtually no interactions occur between themeasurement signals, carried along said conductive element, and thestructural part.
 16. The device of claim 15, wherein: at least thesurface of said conductive element to at least the skin depth, at themeasurement frequencies employed, over the length of the structural partor over the length that is equivalent to the distance between thecorresponding container wall and the lower edge of the structural part,is made from a material of low electrical conductivity and/or highmagnetic permeability.
 17. The device of claim 15, wherein: the surfaceof the conductive element, over the length of the structural part orover the length that is equivalent to the distance between thecorresponding container wall and the lower edge of the structural part,has a roughened surface structure.
 18. The device of claim 15, wherein:the surface of said conductive element, over the length of thestructural part or over the length that is equivalent to the distancebetween the corresponding container wall and the lower edge of thestructural part, has a surface structure, by which the longitudinalinductance of said conductive element is increased.
 19. The device ofclaim 15, wherein: said conductive element, over the length of thestructural part or over the length that is equivalent to the distancebetween the corresponding container wall and the lower edge of thestructural part, has an insulating layer, whose magnetic and/ordielectrical properties are dimensioned such that the length of theelectromagnetic fields is limited to the region at close range to saidconductive element.
 20. A device for determining and/or monitoring thelevel of contents, or the location of the boundary face between twomedia or phases, in a container, having: a signal generating unit, whichgenerates high-frequency measurement signals, said signal generatingunit having an input unit and a conductive element, the measurementsignals being input to said conductive element via said input unit; anda receiving/evaluating unit, which directly or indirectly via thetransit time of the measurement signals, reflected from the surface orboundary face the contents, determines the level of the contents or thelocation of the boundary face in the container, the transition regioninput unit—conductive element is disposed in the plane of said containerwall; said conductive element, at least in the upper region, is madefrom a material of low electrical conductivity and/or high magneticpermeability; and/or said conductive element at least in the upperregion has a roughened surface structure; and/or said conductive elementat least in the upper region has a surface structure by which thelongitudinal inductance of said conductive element is increased; and/orsaid conductive element at least in the upper region has an insulatinglayer, whose magnetic and/or dielectric properties are dimensioned suchthat the length of the electromagnetic fields is limited to the regionat close range to said conductive element.